Inferior Vena Cava Syndrome

Etiology

The etiology of inferior vena cava syndrome (IVCS) depends on the location of the interrupted blood flow. The pathogenesis of IVCS is divided into two events: vena cava obstruction and compression by adjacent structures. The obstruction of the IVC is mostly caused by a primary thrombotic event,[1] either congenital or acquired. Congenital thrombosis of the IVC is often asymptomatic, which is caused by well-developed collaterals. In contrast, acquired etiologies include spontaneous thrombosis of the vessel, either due to external compression or pathological changes of the IVC wall.[1] Thrombosis of the IVC can be due to the propagation of a clot from deep venous thrombosis or from the extension of a thrombus.[1] In addition, conditions that increase the obstruction risk of IVCS are malignancy, pregnancy, infection, obesity, or other intrinsic vein disease. 

Malignancies of organs near the IVC, such as renal cell carcinoma,[3] gastric adenocarcinoma,[4] pancreatic adenocarcinoma,[5] primary or metastatic hepatic malignancies, or tumors of any organ surrounding the IVC, can compress the IVC, leading to obstruction of venous return to the heart. Thus, it causes venous pooling and decreases heart preload. Tumor compression, which can sometimes lead to the development of superior vena syndrome in conjunction with IVCS.[6]

In pregnancy, the distended uterus can compress the IVC, which leads to obstructing the blood flow to the heart and causes increased venous congestion or pooling.[7] Obesity may also be implicated as an etiology of IVCS. A study showed an association between a body mass index (BMI) greater than 30 kg/m² and increased pressure gradients between the thoracic and abdominal vena cava in patients with signs and symptoms of IVCS.[8] 

IVCS can also be due to congenital malformations such as May-Thurner syndrome or Budd-Chiari syndrome. May-Thurner syndrome is a chronic condition in which anatomical variations of vessels in the iliocaval region cause blood flow obstruction.[9] Budd-Chiari syndrome can be classified as primary or secondary. The primary classification refers to any obstruction of the hepatic vein due to a primarily venous process, such as thrombosis or phlebitis. In comparison, secondary relates to compression of the hepatic veins due to external lesions such as cancer.[10]

IVCS can also be caused by iatrogenic processes such as IVC filter placement and venous catheters, which promote thrombosis.[1] In addition, solid organ transplant or surgery, such as hepatic lobe resection, can also increase the risk of thrombosis.[2] Evidence from the literature supports other disease processes, such as cholelithiasis [11] and retroperitoneal hemorrhage.[12], can cause obstruction or compression of the IVC. Hepatic vena cava syndrome, which is associated with poor hygiene and can cause bacterial infection leading to thrombophlebitis of the hepatic veins near the IVC outflow tract, is also recognized as an etiology of IVC syndrome.[13] It has been observed that using Broviac central venous hyperalimentation catheters in pediatric children and teens who need IV therapy, usually for an extended period, can develop IVC syndrome.[14]

Epidemiology

Because IVCS is not a primary diagnosis, accurately quantifying its incidence is difficult due to the variability of underlying pathologies. Reported IVCS shows frequencies of 4 to 15% to an association with deep vein thrombosis.[15] Case reports that have been published stated that gastric cancer, renal cell carcinoma, pancreatic cancer, and liver pathology caused IVCS.[3][4][5][13] However, the exact incidence has never been reported.

Pathophysiology

The inferior vena cava (IVC) returns blood to the heart, along with the superior vena cava (SVC). Obstruction or compression of the IVC reduces venous return to the heart, disrupting hemodynamic equilibrium. Decreased venous return causes hemodynamic instability in several ways. When venous return decreases, blood oxygenation decreases, resulting in hypoxia and subsequent tachycardia. Besides, decreased venous return reduces preload, leading to decreased cardiac output, and the heart compensates by beating rapidly to maintain adequate perfusion to end organs.[16]

Thrombosis of the IVC can result from compression or physical obstruction, leading to venous stasis. Venous stasis is one of the three criteria of Virchow's triad of thrombus formation; the other two are a hypercoagulable state and endothelial damage. The impedance in blood flow causes stasis, which promotes thrombus formation.[17]

The decreased venous return in inferior vena cava syndrome (IVCS) mimics the presentation of hypovolemic shock, with tachycardia, diaphoresis, hypotension, shortness of breath on exertion, dizziness, and cold extremities. IVC congestion causes pallor, ascites, lower extremity peripheral edema, and hypoxia. IVCS also presents with generalized symptoms such as nausea, headache, malaise, and fatigue. In extreme cases, the decreased blood, either through thrombotic or non-thrombotic mechanisms, can lead to altered mental status and even death.[16]

History and Physical

IVCS is not a primary diagnosis but is a consequence of any underlying pathology. As described in the pathophysiology section, the presentation of IVCS is dependent on the patient’s comorbidities and underlying diseases. Accurate diagnosis is based on a thorough history taking and physical examination.

The patient's symptoms are consistent with the pathophysiology of IVCS. It is important to inquire about other signs and symptoms, such as fatigue, dizziness, weight loss, abdominal pain, night sweats, anorexia, palpitations, diaphoresis, and shortness of breath on exertion. In addition, the history taking also has to get deep into previous illness history, including the history of abdominal surgeries, organ transplantation, lower extremity swelling and pain, family and past medical history of coagulopathy, prior deep venous thrombosis (DVT), as well as occupation and lifestyle.

A thorough physical examination will help accurately diagnose IVCS. The vital signs will usually reveal hypotension, tachycardia, and possibly tachypnea with hypoxia. Signs of anemia, such as pallor or pale conjunctiva, might be the earliest indicators of malignant disease and, when accompanied by additional constitutional symptoms of malignancy, can lead to the diagnosis of IVCS. While there are no specific tests with pathognomonic findings of IVCS, certain findings, such as lower extremity edema, signs of DVT and pulmonary embolism, cold and clammy extremities, abnormal neurological exam, hepatomegaly, and abdominal distention, lead to the decrease of venous return, which then impairs the perfusion of end organs.

Evaluation

Duplex ultrasound is the first-line modality for use in a hemodynamically unstable patient. It is a rapid, accurate, and noninvasive modality for investigating the etiology of IVC obstruction. However, interference, ie, obesity, limits the use of ultrasound in identifying the cause of obstruction. Esophagogastroduodenoscopy can also be used to reveal esophageal, gastric, or duodenal pathologies, especially a tumor that compresses the IVC.[4]

CT of the abdomen and pelvis can then be used as an alternative non-invasive modality. Contrast venography, the standard for diagnosis, is used to assess thrombotic obstruction in the abdomen in hemodynamically stable patients. Although it is an invasive procedure, it gives the most accurate findings of IVC obstruction and compression. Magnetic resonance (MR), a noninvasive but expensive imaging modality, can also be used to assess IVC obstruction in hemodynamically stable patients and is replacing CT scans. Etiologies should be urgently identified in hypotensive patients to prevent complications.[1]

Treatment / Management

The guideline treatment of inferior vena cava syndrome (IVCS) has not been clearly described. Therefore, treatment and management are determined by the etiology of the causative lesion and tailored to a patient’s condition. If the lesion is thrombotic, immediate treatment focuses on preventing clot propagation, which could cause pulmonary embolism, and on managing pain, edema, and the resulting hypotension. Either medical or surgical intervention can accomplish this. Medical treatments include anticoagulation using either low-molecular-weight heparin (LMWH), fondaparinux, or direct thrombin inhibitors. These medications reduce the buildup and propagation of the thrombosis but do not eliminate the primary thrombosis.

Endovascular procedures can subsequently be used to deliver thrombolytics to lyse the clot. These can include catheter-directed thrombolysis, pulse-spray pharmaco-mechanical thrombolysis, and angioplasty with or without stent placement, all of which increase IVC patency. Performing such procedures is required within a short period (within 14 days) of the onset of symptoms to minimize complications and decrease mortality rates. Surgical modalities such as thrombectomy, bypass, reconstruction/replacement, and ligation are used as a last resort due to the highly invasive and significant nature of intervention.[1]

If the stent placement is not advisable, placing IVC filters can alleviate symptoms for some time.[6] Recently, the use of IVC filters has increased, especially in advanced-stage cancer patients, in order to prevent pulmonary embolus, although there is no explicit evidence of improved survival rate.[18] Temporary IVC filters are usually used in cancer patients during systemic chemotherapy.[19](B2)

If lesions are due to non-thrombotic etiologies, such as malignancy, treatment is directed at managing the underlying cause of the compression. This may include surgery, chemotherapy, radiation, or a combination of these. Resection is a surgical option to remove the tumor compression. However, resection cannot be done in unstable patients; thus, palliative care is provided. Another option is to place an intravascular stent or perform surgical bypass grafting, which increases the patency of the IVC to alleviate symptoms.[1][20] Recanalization of the occluded veins is usually done by implanting the metallic stents into the IVC from the superior vena cava via the right atrium.[21](B3)

IVCS patients of intrahepatic obstruction due to malignant hepatic enlargement are usually treated using strip radiotherapy to the intrahepatic IVC, with or without a hepatic arterial infusion of chemotherapy.[22] The IVC obstruction is generally managed by crossing the tumorous lesion with either a guidewire or Brockenbrough needle along with a Mullins sheath assembly, and then a balloon dilatation is performed with the help of an Inoue or Mansfield balloon.[23] In some mild compression etiologies like pregnancy, physical maneuvers to move the uterus away from the IVC can be applied.[7]

Differential Diagnosis

IVCS is characterized by tachycardia, hypotension, tachypnea, hypoxemia, and shortness of breath. The differential diagnosis of IVCS is broad, mainly because it is rarely ever diagnosed as a primary disease process. The differential diagnosis of IVCS is: 

• Chronic venous insufficiency
• Shock
• IVC compression
• Malignancy [5]
• Deep vein thrombosis
• Iliocaval syndrome
• Aortocaval syndrome [7]

Prognosis

The prognosis of IVCS depends on the underlying patient condition, including hemodynamic status, the severity of compression or venous obstruction, the grade of malignancy, and prior comorbidities. The outcome of patients who have inferior vena cava thrombosis overall relates to the embolic risk associated with DVT. If the IVC is occluded, pulmonary embolism does not present a significant risk. However, if the IVC lumen remains, embolization may occur.

Complications

Complications of inferior vena cava syndrome (IVCS) depend on the underlying comorbidity and patient's risk factors for the following, but include:

• Pulmonary embolism (PE) [24]
• Deep vein thrombosis [25]
• Chronic venous insufficiency (CVI)
• Post-thrombotic syndrome (PTS) progressing to venous ulceration, venous gangrene
• Hemodynamic instability leading to cardiac arrest and possibly death [1]